ABA型三嵌段共聚物乳胶粒的微相结构调控及其胶膜的力学性能研究

发布时间：2018-03-20 20:18

  本文选题：RAFT细乳液聚合　切入点：界面亲和力　出处：《浙江理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：相比阴离子聚合,“活性”自由基(细)乳液聚合在制备嵌段共聚物方面具有突出优点。采用该技术,已成功制备多种ABA型三嵌段共聚物热塑性弹性体,且其力学性能呈现热塑性弹性体的典型特征。然而,对上述材料性能的研究多局限于聚合物的溶剂膜,较少涉及其乳胶膜。论文采用对称结构的RAFT试剂,以“两步法”得到了两端聚苯乙烯(PSt)嵌段分子量为30K g/mol,中间嵌段链结构不同的多种三嵌段共聚物胶乳,调控了胶乳的微相结构,并研究了胶乳的成膜性能,膜的微相结构和力学性能,得到如下结论:1、采用两亲性对称结构大分子RAFT试剂(macroRAFT)和对称结构小分子RAFT试剂(ATTCA)均能精确调控三嵌段共聚物的链结构。两阶段单体转化率均在90%以上,聚合物分子量随转化率线性增高,呈现“活性”聚合物反应的特征,但产物分子量分布较宽,分子量分布指数达3.5。2、三嵌段共聚物胶乳的微相结构受嵌段比和胶体界面对嵌段亲和力的共同影响:Ⅰ:采用macroRAFT试剂,制备“聚苯乙烯-聚丙烯酸丁酯-聚苯乙烯(PSt-b-PnBA-b-PSt)”时,因两端PSt嵌段与macroRAFT试剂的亲水嵌段相连,受界面亲和力大,因此得到的30K-90K-30K和30K-160K-30K两种PSt-b-PnBA-b-PSt嵌段共聚物胶乳均呈现典型的“核(PnBA)-壳(PSt)”结构,但壳的厚度随PnBA链长的增大而减小。Ⅱ:改以ATTCA制备PSt-b-PnBA-b-PSt时:一方面,因共聚物两端PSt嵌段不再连接亲水嵌段,所受界面亲和力减小;另一方面,PnBA极性高,亲水性强于PSt,因此PSt链段向乳胶粒内核聚集,所得共聚物的PnBA嵌段富集于粒子表面。Ⅲ:采用macroRAFT试剂控制聚合反应,当中间嵌段为丙烯酸丁酯与丙烯酸乙酯的共聚物时(PnBA-co-PEA),亲水性更强的EA链节提高了胶体界面对P(nBA-co-EA)嵌段的亲和力,使其与PSt嵌段在界面处竞争富集,粒子不再呈现典型的“核-壳”结构。此时,随着P(nBA-co-EA)链长的增加以及EA单元比例的增大,粒子表面可观察到更多的中间嵌段微相。3.胶乳的成膜能力受微相结构和中间嵌段共聚组成的共同影响,呈现如下规律:Ⅰ:随着PSt-b-PnBA-b-PSt“核-壳”胶乳PSt壳层厚度的减小,壳层的玻璃化温度降低,因此30K-160K-30K胶乳可室温成膜,成膜能力高于30K-90K-30K;Ⅱ:链结构为30K-90K-30K时,因界面亲和力P(nBA-co-EA)PnBA,因此P(nBA-co-EA)最易在胶体界面富集,其较低的玻璃化温度使得PSt-b-P(nBA-co-EA)-b-PSt胶乳成膜能力最高,而PSt-b-PnBA-b-PSt最低,甚至室温难以成膜。4.提高退火温度,虽可推动微相结构向热力学稳态结构演化,但结果表明即便退火温度高达160 OC,退火时间48 h,膜内聚合物仍难达到热力学平衡态结构。5.相比于溶剂膜,相近共聚组成的胶乳膜具有更高的弹性模量,但屈服强度和断裂伸长率劣于前者。胶乳膜的“应力-应变”曲线中未出现“应力增强”现象,这与胶乳膜内嵌段共聚物的中间嵌段较少形成跨相的桥梁连接(bridge)有关。
[Abstract]:Compared with anionic polymerization, "active" radical (fine) emulsion polymerization has outstanding advantages in the preparation of block copolymers. By using this technique, a variety of ABA triblock copolymer thermoplastic elastomers have been successfully prepared. The mechanical properties of these materials are typical of thermoplastic elastomers. However, most of the studies on the properties of these materials are limited to the solvent membranes of polymers, and less to their latex films. The RAFT reagent with symmetric structure is used in this paper. By "two-step method", a variety of triblock copolymers with a molecular weight of 30 kg / mol and different intermediate block chain structures were obtained. The microphase structure of the latex was regulated, and the film forming properties of the latex were studied. The microphase structure and mechanical properties of the film, It is concluded that the chain structure of triblock copolymers can be accurately regulated by using amphiphilic macromolecule RAFT reagent and symmetric small molecular RAFT reagent ATTCA. The monomer conversion rates of the two stages are above 90%. The molecular weight of the polymer linearly increases with the conversion, showing the characteristics of "active" polymer reaction, but the molecular weight distribution of the product is relatively wide. The molecular weight distribution index was 3.5.2. The microphase structure of the triblock copolymer latex was affected by the block ratio and the affinity of the colloid interface to the block. 鈪，

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